1. Field of the Invention
The present invention relates to a hydraulic accumulator for accumulating pressurized liquid, and more particularly to a bellows-type hydraulic accumulator whose interior is sectioned into a gas chamber, in which pressurized gas is enclosed, and a liquid chamber communicating with the exterior, by means of a bellows.
2. Description of the Related Art
Accumulators of the above-described type are disclosed in, for example, Japanese Patent Application Laid-Open (kokai) Nos. 2000-356201, 2000-320501, and 2000-249101, and German Patent Publication No. DE19954326A1. In these conventional accumulators, a hydraulic accumulator structure is established by provision of a shell defining a pressure space, and a bellows sectioning the pressure space into a gas chamber in which pressurized gas is enclosed and a liquid chamber communicating with the exterior.
However, a potential problem in relation to the above-described conventional accumulators is that, when the bellows is broken, not only is the accumulator function itself lost, but also pressurized gas enclosed in the accumulator is prone to flow out of the accumulator into a hydraulic circuit in which the accumulator is employed.
In view of the foregoing problems with the conventional technology, an object of the present invention is to provide a bellows-type hydraulic accumulator which, even when bellows happen to be broken, is able to not only retain the accumulator function itself, but also prevent pressurized gas enclosed in a gas chamber from flowing out of the accumulator into a hydraulic circuit to which the accumulator is applied.
To achieve the above object, according to a first aspect of the present invention, there is provided a bellows-type hydraulic accumulator comprising: a main shell forming a pressure space; a bellows unit which is disposed in the pressure space and whose first end is fixedly secured to a first end wall of the main shell, the bellows unit sectioning the pressure space into an outer chamber serving as a gas chamber in which pressurized gas is enclosed, and an inner chamber serving as a main liquid chamber communicating with a liquid port formed in the first end wall of the main shell; an auxiliary shell disposed in the main liquid chamber and fixed to the main shell, the auxiliary shell having an auxiliary liquid chamber formed therein and communicating with the liquid port of the main shell; and a movable wall member disposed inside the auxiliary shell and sectioning the auxiliary liquid chamber into a first interior portion communicating with the liquid port and a second interior portion communicating with the main liquid chamber via a communication passage formed in the auxiliary shell.
According to a second aspect of the present invention, there is provided a bellows-type hydraulic accumulator comprising: a main shell defining a pressure space; a bellows unit which is disposed in the pressure space and whose first end is fixedly secured to a first end wall of the main shell, the bellows unit sectioning the pressure space into an inner chamber serving as a gas chamber in which pressurized gas is enclosed, and an outer chamber serving as a main liquid chamber communicating with a first liquid port formed in a second end wall of the main shell; an auxiliary shell disposed outside the main shell and fixed to the main shell, the auxiliary shell having an auxiliary liquid chamber formed therein and communicating with the first liquid port; and a movable wall member disposed inside the auxiliary shell and sectioning the auxiliary liquid chamber into first and second interior portions, the first interior portion communicating with a second liquid port that is formed in a bottom wall portion of the auxiliary shell opposite the main shell, the second interior portion communicating with the main liquid chamber via the first liquid port.
In the accumulators according to the first and second aspects of the present invention, a hydraulic accumulator structure is constituted by the main shell and the bellows unit; and another hydraulic accumulator structure is constituted by the main shell, the auxiliary shell, and the movable wall member. Therefore, even when the bellows breaks, not only does the accumulator itself retain its function, but also pressurized gas enclosed in the gas chamber of the accumulator can be prevented from accidentally flowing out of the accumulator (in other words, prevented from flowing into a hydraulic circuit in which the accumulator is employed).
The accumulator according to the first aspect of the present invention can be constructed compactly, because the auxiliary shell and the movable wall member are located within the bellows inside the main shell. The accumulator according to the second aspect of the present invention can be constructed by utilizing the existing shell and bellows structure as a base.
Preferably, in the accumulator according to the first aspect of the present invention, maximum and minimum volumes of the second interior portion are respectively set in such a manner that, when an amount of liquid corresponding to a difference between the maximum and minimum volumes is fed from the auxiliary liquid chamber into the main liquid chamber, a gap remains between a second end of the bellows unit, opposite the first end thereof, and a second end wall of the main shell, opposite the first end wall thereof, in order to avoid a possible impact therebetween and such that, when the above-mentioned amount of liquid is fed from the main liquid chamber into the auxiliary liquid chamber, a gap remains between the second end of the bellows unit and an end wall of the auxiliary shell in order to avoid a possible impact therebetween.
Preferably, in the accumulator according to the second aspect of the present invention, maximum and minimum volumes of the second interior portion are respectively set in such a manner that, when an amount of liquid corresponding to a difference between the maximum and minimum volumes is fed from the auxiliary liquid chamber into the main liquid chamber, a gap remains between a second end of the bellows unit, opposite the first end thereof, and the first end wall of the main shell, in order to avoid a possible impact therebetween and such that, when the above-mentioned amount of liquid is fed from the main liquid chamber into the auxiliary liquid chamber, a gap remains between the second end of the bellows unit and the second end wall of the main shell, opposite the first end wall thereof, in order to avoid a possible impact therebetween.
In these cases, the stroke of the bellows unit is determined by means of the amount of liquid permitted to flow into and out of the second interior portion; and an overstroke of the bellows unit can be restrained so as to avoid an impact between the second end of the bellows unit and an end wall opposing thereto, whereby effective protection of the bellows unit can be achieved.
In the accumulator according to the first aspect of the present invention, preferably, the auxiliary shell includes a tubular wall portion defining a cylinder bore, and a bottom wall portion serving as a partition between the cylinder bore and the main liquid chamber; and a hole serving as the communication passage is formed in the bottom wall portion. In this case, the auxiliary shell can be constructed simply and at low cost.
In the accumulator according to the first aspect of the present invention, more preferably, the auxiliary shell includes a tubular wall portion defining a cylinder bore, and a bottom wall portion serving as a partition between the cylinder bore and the main liquid chamber; the movable wall member is constituted by a piston that is fitted in the cylinder bore in a liquid-tight and slidable manner; and a hole serving as the communication passage is formed in the bottom wall portion. In this case, the auxiliary shell and the movable wall member (piston) can be constructed simply and at low cost.
Preferably, a stroke of the piston is limited by the bottom wall portion of the auxiliary shell and the first end wall of the main shell. In this case, the stroke of the piston can be limited by the bottom wall portion of the auxiliary shell and the first end wall of the main shell, and the sliding movement of the piston can be precisely restrained by means of a mechanical stopper (the auxiliary shell""s bottom wall portion and the main shell""s first end wall) at either the low-pressure side or the high-pressure side.
Preferably, the bellows unit includes a bellows and a movable plate connected with an end of the bellows corresponding to the second end of the bellows unit; and the accumulator further comprises an annular sealing member mounted on at least one of opposing surfaces of the movable plate and the bottom wall portion of the auxiliary shell and adapted to be brought into and out of liquid-tight contact with the other of the opposing surfaces when the movable plate is moved toward and away from the bottom wall portion of the auxiliary shell, whereby the hole in the bottom wall portion of the auxiliary shell is separated from and communicated with the main liquid chamber and vice versa.
When the pressure of the main liquid chamber between the bellows and the auxiliary shell is lowered as a result of failure of the movable wall member in sectioning the interior of the auxiliary shell, the annular sealing member isolates the main liquid chamber from the hole formed in the bottom wall portion of the auxiliary shell (shuts off the communication passage between the main liquid chamber and the hole of the bottom wall portion of the auxiliary shell), to thereby prevent overcontraction (overcollapse) of the bellows.
Preferably, the piston assumes a bottomed tubular shape. In this case, the piston can be reduced in weight while securing the necessary length of the outer-circumferential-surface guide.
Preferably the bellows of the bellows unit is metallic. In this case, liquid pressurized at high pressure can be accumulated in the main liquid chamber.